This application is based on and claims priority from Japanese Application No. HEI 3-88873 filed Oct. 3, 1991, the disclosure of which is incorporated herein by reference.
The invention relates to a sealed case which protects an inside of the case from the outside environment, such as a waterproof case of an apparatus which needs a waterproof and dampproof structure.
One example of a sealed case is an exterior case of a camera which has a waterproof and dampproof structure. Such a sealed case has to be inspected for airtightness. For example, it has been known to measure a pressure change on the inside of the case as a method of inspection. That is, a communication hole is provided in advance through an outer wall between the inside and the outside of the case, and a change in the pressure of the inside is measured by a barometer after taking air from or sending compressed air into the inside of the case. At this time, if the air leaks from unexpected holes or spaces so that the case is incompletely sealed, the pressure of the inside of the case gradually approaches the pressure of the atmosphere. Thus, the airtightness is inspected by detecting the presence or absence of the pressure change.
With respect to the conventional sealed cases, one type uses as the communication hole an opening provided for other purposes which is opened or closed by a kind of cap such as a dry cell cover, and another type uses a communication hole provided exclusively for the airtightness inspection, which is opened or closed by a cap.
However, the conventional sealed cases have the following problems. The cap opening or closing the hole for the inspection cannot be inspected itself for airtightness. Also, the cap has to be taken off and put on before and after the inspection. Still further, connection means for connecting the hole and a tube are needed to take out or send the air, and the connection means must avoid leaking air from a connecting portion.